Hydrogenation reactions are frequently carried out in the presence of a pyrophoric catalyst such as Raney nickel. This presents a serious difficulty because flammable liquids such as methanol or ethanol are often used as hydrogenation solvents. The removal of the catalyst from the reaction mixture after the hydrogenation reaction is complete, presents serious difficulties. Generally the reaction mixture is passed through a filter, the catalyst is filtered out and removed in a closed circuit.
Handling of the resultant catalyst presents difficulties and the commonly used multiplate filters, which necessitate generation of hazardous dry material, require extensive safety precautions, and extended operation times to facilitate safe removal of the catalyst.
U.S. Pat. No. 4,021,354 describes a pressure filter comprising an outer casing having a filter basket supported therein. The filter basket comprises a tubular imperforate metallic shell with a sintered stainless steel filter disc welded to the lower end of the shell. Such a pressure filter is not suitable for use with fine metallic catalyst as the sintered disc readily clogs during operation. Removal of catalyst from the pores requires reverse flow of water and frequent use of acid to dissolve trapped material.
DE-A-3 136905 describes a pressure filter including a sieve basket of the same type as that described in U.S. Pat. No. 4,021,354 and similar disadvantages apply.
There is therefore a need for an improved cost effective filter apparatus for removing a pyrophoric catalyst which will overcome these problems.